Somatic cell hybrids, generated by fusion of erythroid cells and established cell lines, will be used to obtain continuously replicating cells capable of globin synthesis. These would then be utilized to study regulation of expression of the globin genes. In addition, human-mouse hybrids containing one or more human chromosomes would be studied for localization of human globin structural genes. The studies leading to the chromosome assignment of the alpha and beta globin structural genes will be continued. Somatic cell hybrids which coexpress both mouse and human globin chains will be studied to attempt to learn the factors controlling expression of the globin genes.